Because of increased interest in automobile safety and passive restraint systems for the protection of the driver or passengers, inflatable airbag assemblies have become well known in the art. These inflatable airbag assemblies typically have a gas supply means and an airbag to which the gas is delivered. In the event of a collision, the gas supply means activates and inflates the airbag, thus providing a protective cushion for the vehicle's occupants. The inflated airbag, acting as a cushion, prevents or reduces injuries to the vehicle's occupants caused by violent contact with the inner surfaces of the vehicle.
These airbag systems often use a gas supply means containing gas producing substances. When the vehicle becomes involved in a collision of a predetermined magnitude, the gas producing substances are activated, often by burning, to rapidly inflate the airbag. Because of the rapid combustion, the produced inflating gases may reach temperatures of about 1100.degree. F. or higher. These high temperature gases may be detrimental to the integrity of the airbag fabric. For example, the melt temperature of nylon is about 480.degree. F. When nylon is used as the airbag fabric, then, the airbag may melt and thus lose function. Further, nylon loses strength at elevated temperatures. A temperature of 200.degree. F., for example, reduces the high strain rate breaking strength of nylon by about 25 percent. Accordingly, the high temperature gases used to inflate conventional airbag systems present significant risks of airbag failure.
It is therefore known in the art to provide a type of heat shield in proximity to the gas supply means. U.S. Pat. No. 3,843,151 discloses the use of a particle screen device made of a wire mesh screen bag, or a porous pipe or cylinder, to prevent hot particles from contacting the inner surface of the airbag. Around the particle screen device, the '151 patent further contains a sound reducing bag made of wire mesh, fibered glass, asbestos, nylon, or a plastic material. In combination, the particle screen device and sound reducing screen prevent hot particles from the gas generator from contacting the airbag and reduce the level of sound resulting from the rapid expansion of inflating gases.
U.S. Pat. No. 3,900,210 discloses an airbag system with an inner, porous bag made of a knit material such as nylon or polyester. The inner bag is disclosed to reduce the sound resulting from inflation of the airbag and absorb heat and smoke produced from the use of the inflatable gas system.
U.S. Pat. No. 5,172,933 discloses an airbag system having a U-shaped fabric sleeve with two open ends disposed in proximity to the gas supply means. The U-shaped sleeve, which may have apertures on its surface, provides for the lateral flow of a substantial quantity of gases into the surrounding airbag through the open ends.